PERVAPORATIVE TRANSPORT MODELING IN A TERNARY-SYSTEM - ETHYLTERTIARYBUTYLETHER ETHANOL/POLYURETHANEIMIDE/

The study deals with the analysis of diffusion and mass transfer model ling during pervaporation in a true ternary system involving a polar l iquid mixture (ETBE/EtOH) and a polar block copolymer (polyurethaneimi de or PUI). A survey of methods of pervaporative transfer modelling in ternary systems is first developed. From differential permeation expe riments carried out with both pure liquids, it appears that both perme ants obey a Fickian law. Moreover, the diffusional behaviour is consis tent with Long's model, which has thus been assumed for the related te rnary system. An extension of the Brun's model is then derived, which takes into account the diffusion coupling as well the significant devi ation from sorption ideality. From a practical point of view, the calc ulated values of fluxes show generally good agreement with the experim ental results, although a small deviation occurs for mixtures of low e thanol content. Diffusion coefficients of both pure solvents correspon ding to transient or steady state are compared. A very good agreement is found for the aprotic permeant (ETBE), whereas the diffusion coeffi cient of ethanol in transient state is only the quarter of the value c orresponding to steady state. The results are discussed in comparison with related investigations in the literature, involving specific liqu id-polymer interactions.